Physics 106N - How Things Work - Spring, 1997
Study Questions for Final Exam
Section 1.1 - Falling Balls
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What is the difference between velocity and acceleration?
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What is the difference between weight and mass?
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How does an object’s mass affect its acceleration?
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What forces are acting on a freely falling object as it heads upward;
as it heads downward?
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Why do all freely falling objects accelerate downward at the same rate?
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Why doesn’t the horizontal component of an object’s velocity change
as that object falls?
Section 1.2 - Ramps
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Which object experiences each force when the two objects push against
one another?
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What must you do to an object to do work on it?
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What is the relationship between work and energy?
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Why does an object’s gravitational potential energy increase as its
altitude increases?
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When a object slides freely on a ramp, what is the direction of the
net force on that object?
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How does employing mechanical advantage to perform a task affect the
work you do?
Section 1.3 - Seesaws
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What is the difference between angular velocity and angular acceleration?
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What effect does a torque have on an isolated object?
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About what point does an isolated object rotate?
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How can you use a force to produce a torque?
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How can you use a torque to produce a force?
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How does an object’s moment of inertia affect its angular acceleration?
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Why must two objects be on opposite sides of a seesaw to balance one
another?
Section 1.4 - Wheels
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How do the two types of friction, static and sliding, differ from one
another?
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How can sliding friction bring a moving object to rest without violating
the conservation of energy?
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Why does the wheel of a toy wagon begin to turn when you pull that
wagon forward?
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Why does an automobile accelerate forward when the engine begins to
turn its wheels?
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What is the difference between force and momentum?
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When you throw a baseball forward, where does the ball’s momentum come
from?
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When you spin a toy top, where does the top’s angular momentum come
from?
Section 11.1 - Electronic Air Cleaners
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Why do tiny particles descend so slowly through the air?
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How do the forces between two electric charges depend on the types
of charges and on their separation?
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Where is the charge located on an electrically charged metal object?
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Why are thin wires or sharp points so effective for transferring charge
to the air or to dust particles in the air?
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What holds an electrically charged balloon against the wall?
Section 11.2 - Xerographic Copiers
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Why don’t all the electrons in a solid travel in the lowest energy
level?
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How do an insulator and a conductor differ?
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What role does electric field play in the force that one electric charge
exerts on another electric charge?
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How does light exposure cause a semiconductor to transform from an
insulator to a conductor?
Section 11.3 - Magnetically Levitated Trains
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How do the forces between two magnetic poles depend on the types of
poles and on their separation?
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What is the net magnetic pole of a grapefruit?
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What role does magnetic field play in the force that one magnetic pole
exerts on another magnetic pole?
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How can an electric charge produce a magnetic field?
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How can a magnet produce an electric field?
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What can you do to piece of aluminum to make it become magnetic without
touching that aluminum?
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Why does an electric current that’s flowing on its own through a copper
ring gradually diminish as time passes?
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Why does an electric current that’s flowing on its own through a superconducting
ring continue to flow steadily as time passes?
Section 12.1 - Flashlights
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Why must there be a complete electric circuit before current will flow
steadily between a battery and a light bulb?
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What is the difference between current and voltage?
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What effect does a battery have on a current that flows through it?
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Why is the direction in which current flows through a battery important?
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How can two different electric currents, with different amounts of
current and different voltages, deliver identical amounts of power to their
respective light bulbs?
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Why can a battery either provide or consume power, while a light bulb
can only consume power from the circuit it’s in?
Section 12.2 - Electric Power Distribution
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How does increasing the current through a wire affect the power wasted
in that wire?
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What becomes of the power wasted in a wire?
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How can two different currents in two identical wires deliver equal
amounts of electric power to their destinations while wasting different
amounts of power in those wires?
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How does a transformer transfer power from one circuit to another without
allowing any charges to pass between those circuits?
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Why do a transformer only work with alternating current?
Section 12.3 - Electric Power Generation
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How does moving a magnetic past a coil of wire affect the current passing
through that coil?
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Why does an electric generator need something to keep it turning, even
if its bearings are essentially frictionless?
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How does the energy stored in a fossil fuel reach your home electrically?
What forms does it take along the way and how is it transferred or transformed
as it moves along?
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How does a diode prevent current from flowing through it in one direction?
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How does light allow a diode to provide electric power?
Section 12.4 - Electric Motors
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What does the rotor of a motor continue to turn indefinitely?
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Why does an electric motor powered by direct current need some sort
of internal electric switch to keep turning?
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How can the aluminum rotor of an induction motor experience magnetic
forces even though aluminum is a non-magnetic metal and there are no electric
connections to the rotor?
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What determines the direction in which an induction motor rotates?
Section 12.5 - Tape Recorders
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In what way is iron intrinsically magnetic?
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Why does a large piece of iron normally appear non-magnetic?
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How does the presence of a nearby magnetic pole cause a piece of iron
to exhibit its intrinsic magnetism?
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Why do some magnetic materials remain permanently magnetized?
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How does the surface of a magnetic tape represent sound?
Section 13.1 - Audio Amplifiers
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Why does an audio amplifier need a source of power?
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Why is it important that the current an amplifier sends through its
output circuit be proportional to the current passing through its input
circuit?
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How does the voltage drop a current experiences as it passes through
an electric resistor depend on how well that resistor conducts electricity?
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How does a capacitor store electrostatic potential energy without acquiring
any net electric charge?
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How does electric charge on the gate of an MOSFET control the flow
of current between its source and drain?
Section 13.2 - Computers
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How can electric charge represent a bit of information?
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How can magnetism be used to represent information?
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If two electronic components are connected in parallel to one another,
how is the total current they’re carrying related to the current through
each component?
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If two electronic components are connected in series with one another,
how is the total current they’re carrying related to the current through
each component?
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Why does a computer’s size affect the speed with which it can perform
calculations?
Section 14.1 - Radio
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Why does a tank circuit’s energy transform back and forth rhythmically
between electrostatic potential energy and magnetic potential energy?
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How does the movement of charge on one antenna affect the charge on
another nearby antenna?
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Why does an electromagnetic wave always have both an electric field
and a magnetic field.
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What produces the electric field in an electromagnetic wave?
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What produces the magnetic field in an electromagnetic wave?
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How does a radio station use amplitude modulation to instruct a radio
receiver what to do with its speaker?
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How does a radio station use frequency modulation to instruct a radio
receiver what to do with its speaker?
Section 14.2 - Television
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How does electric current flow between the back of a picture tube and
its front surface?
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How does electric energy become light energy in a television?
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How does a magnetic field affect a moving electric charge?
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How is a television image constructed on its screen?
Section 14.3 - Microwave Ovens
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What distinguishes microwaves from radio waves and visible light?
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How do metals reflect electromagnetic waves?
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Why does water become hot when exposed to microwaves?
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How does a C-shaped piece of metal act as a microwave tank circuit?
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Why is the antenna in a microwave oven only a few centimeters long?
Section 15.1 - Sunlight
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How does a hot surface produce light?
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Why does light slow down when it enters matter?
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Why does the surface of a transparent material partially reflect light?
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Which way does light bend when it enters the surface of a transparent
material?
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Why does white light separate into colors after going through cut crystal
or a diamond?
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Why does a thin transparent film often appear colored?
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Why do many good sunglasses block horizontally polarized light?
Section 15.2 - Fluorescent Lamps
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Why are red, green, and blue the primary colors of light?
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Why is incandescent light energy inefficient?
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Why must the electrodes of a typical fluorescent lamp be hot in order
to sustain the electric discharge in the mercury gas?
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What determines which wavelengths of light are emitted by a low pressure
gas discharge?
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How does high pressure in a gas discharge affect the wavelengths it
emits?
Section 15.3 - Lasers
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How does coherent light differ from incoherent light?
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How does a laser produce coherent light?
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What does it mean to amplify light?
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Why does a laser oscillator need several mirrors to operate?
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Why does a laser need a great many identical excited atomic or atomic-like
systems to operate?
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How do some lasers store energy and then produce incredibly bright
pulses of light?
Section 16.1 - Cameras
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Why does the distance from an object to a converging lens affect the
distance from that lens to the real image it forms?
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Why is a real image only formed at a specific distance from a converging
lens?
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How does the focal length of a converging lens affect the distance
from it to the real image it forms?
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Why does a small lens have a greater depth of focus than a large lens?
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What color problems does a single element converging lens have?
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What change occurs on a piece of photographic film when that film is
exposed to light?
Section 16.2 - Telescopes and Microscopes
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When you use a converging lens as a magnifying glass, where is the
image located?
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What part does the objective of a telescope or microscope play in providing
an enlarged view of the object you’re observing?
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What part does the eyepiece of a telescope or microscope play in providing
an enlarged view of the object you’re observing?
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Why is a large-aperture telescope able to resolve finer details than
a small-aperture telescope?
Section 16.3 - Compact Disc Players
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Why is it important to use a laser rather than a conventional light
source in a compact disc player?
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Why is the wavelength of the laser light shorter inside the disc than
in the air?
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How does interference improve the player’s ability to distinguish ridges
in the aluminum layer from valleys?
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How does reversing the polarization of the laser light prevent it from
returning to the laser diode?
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Why do horizontally and vertically polarized lights bend differently
when entering or exiting a birefringent crystal?
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When does total internal reflection occur?
Section 17.1 - Knives and Steel
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What is the relationship between stress and strain?
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What happens inside a metal when you bend it gently and it then returns
to its original shape when you let go?
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What happens inside a metal when you bend it severely and it does not
return to its original shape when you let go?
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How does the inclusion of carbon in steel make it more difficult to
deform that steel permanently?
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Why does steel suddenly lose its magnetism when you heat it red hot?
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How does the speed with which carbon steel is cooled affect its hardness?
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Why can’t common stainless be hardened by carbon and heat treatment?
Section 17.2 - Windows and Glass
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How are the atoms in a glass arranged differently than in a crystal?
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How is a glass formed?
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Why is quartz so good at forming glasses?
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Why is tempered glass so difficult to break?
Section 17.3 - Plastics
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What are the molecules in a plastic like?
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Why do plastics always contain amorphous regions?
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What sorts of molecular motions account for the five regimes of plastic
behavior?
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Why do only certain plastics melt?
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How are plastics formed?
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Why are plastics with straight polymer chains extremely strong?
Section 18.1 - Nuclear Weapons
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In what sense do the two forces present in an atom’s nucleus oppose
one another?
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Why do large nuclei often release energy when they break in half?
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Why is the short range character of the nuclear force essential to
the existence of spontaneous fission?
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Why is uranium-235 suitable for a fission bomb while uranium-238 is
not?
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Why is it so difficult to separate uranium-235 from uranium-238?
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"Critical Mass" is a misnomer—what arrangement of materials
is actually required for an explosive fission chain reaction to occur?
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How does a fusion bomb differ from a fission bomb?
Section 18.2 - Nuclear Reactors
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Why doesn’t a nuclear reactor explode the instant its core exceeds
critical mass?
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How do "control rods" keep a reactor’s chain reaction from
getting too intense?
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How can a thermal fission reactor operate on natural uranium?
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How does a moderator slow neutrons down?
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Why does a fast fission reactor require enriched uranium?